A new TDCS adaptive threshold selection algorithm based on Otsu guidelines is proposed. In this algorithm, the spectral amplitude of the channel sensing are gray mapped, the spectrum grayscale is divided into background noise and interference by using Otsu guidelines, the best classification threshold is determined as the TDCS interference-rejecting decision threshold as well. The method is of strong adaptive capacity based on the perception of the channel and can be used to search the best decision threshold dynamically. Simulation results show that, the proposed method demonstrates superior performance than the traditional methods in the changing of channel background noise, especially when the background noise is increased to a certain extent, the communication system with traditional fixed threshold method will not work properly, but the use of the proposed method still makes the system performance good.